Identification of graminicide-resistant johnsongrass (Sorghum halepense)

Abstract

Resistance to fluazifop-P and quizalofop-P, (aryloxyphenoxypropionates) and sethoxydim (cyclohexanedione) was identified in 2 populations of johnsongrass in both field and greenhouse studies. The cropping history (1983–1991) of the sites indicated 1 or more annual applications of a graminicide (primarily fluazifop-P) since the early 1980s. Under field conditions, control of resistant seedling and rhizome johnsongrass (R91F) with fluazifop-P, quizalofop-P, fenoxaprop-ethyl, and sethoxydim was less than 35%. Clethodim provided up to 80% control of R91F. Under greenhouse conditions, ratios (R/S) of the I50values (amount of herbicide required to inhibit plant growth by 50%) of resistant (2 sites: R91F and R91S) to susceptible (S91H) seedling (20–30-cm height) plants were > 388 (fluazifop-P), > 15 (quizalofop-P), and from 2.3 (R91S) to 3.4 (R91F) (both sethoxydim). For rhizome (30–45 cm height) plants, the R/S ratios were > 388 (fluazifop-P), > 16 (quizalofop-P), and 2.8 (R91S) to 8.5 (R91F) (both sethoxydim). Labeled rates (in kg ai ha−1) of fluazifop-P (0.10 and 0.21), quizalofop-P (0.039 and 0.08), and sethoxydim (0.21 and 0.21) were applied on seedling and rhizome plants, respectively, and resulted in little or no control of resistant johnsongrass. Greenhouse studies indicated registered rates of clethodim (0.10 and 0.14 kg ai ha−1for seedling and rhizome plants, respectively) effectively controlled the resistant populations, but tolerance was measured for both seedling and rhizome plants at sublethal doses (down to 0.007 and 0.009 kg ai ha−1, respectively), with I50ratios ranging from 1.5 (R91S) to 2.1 (R91F) for seedling plants and 4.5 (R91S) to 4.8 (R91F) for rhizome plants. Control of resistant seedling and rhizome johnsongrass under field conditions was adequate with glyphosate at 0.84, glufosinate at 0.84, and sulfosate at 0.84 kg ai ha−1, indicating no cross-resistance.

Modeling Investments in Seeds, Clonal Offspring, and Translocation in a Clonal Plant

“…However, high levels of genetic diversity in clonal plant populations indicate that seedlings do establish (Ellstrand and Rouse 1987, Alpert et al 1993, Eriksson and Bremer 1993, Widen et al 1994, Schläpfer and Fischer 1998 and that sexual offspring may be important to genet fitness (Bell 1985, Stearns 1985, Kondrashov 1988, Ladle 1992, Lynch et al 1993). In addition, seeds that colonize new habitats may contribute disproportionately to genet fitness; the success of clonal plants as weeds (Lapham 1985, Santos et al 1997, Smeda et al 1997, Yenish et al 1997 and invasive species (Smith 1985, Cudding and Stone 1990, Room 1990, Soukupova 1992, Schmid and Weiner 1993, Philbrick and Les 1996 suggests that when colonization is successful, colossal payoffs ensue. Finally, in some cases ramets may incur few or no costs from producing seeds (Reekie and Bazzaz 1987, Wikberg et al 1994.…”

Genetic Resistance to Acetyl‐Coenzyme A Carboxylase‐Inhibiting Herbicides in Grain Sorghum

“…(Heap, 2010). Only a few peer-reviewed journal articles have been published on these populations Burke et al, 2006a, b;Smeda et al, 1997Smeda et al, , 2000 along with some non-peer-reviewed publications (Marles and Devine, 1993;Obermeier, 1998). Two of these populations have very low resistance factors to both APP and CHD herbicides and the other two populations have high resistance factors to APP herbicides but very low resistance factors to CHD herbicides.…”

“…Two of these populations have very low resistance factors to both APP and CHD herbicides and the other two populations have high resistance factors to APP herbicides but very low resistance factors to CHD herbicides. The resistance mechanisms were reported as overproduction of ACCase , target site resistance that provides cross resistance (Burke et al, 2006a), and target site resistance that provides very little cross resistance (Obermeier, 1998;Smeda et al, 1997). Neither of the target site resistance reports provided sequence information for a casual mutation.…”

“…populations with resistance to ACCase lierbicide have been reported and eight were described as Johnsongrass \S. The resistance mechanisms were reported as overproduction of ACCase (Bradley et al, 2001), target site resistance that provides cross resistance (Burke et al, 2006a), and target site resistance that provides very little cross resistance (Obermeier, 1998;Smeda et al, 1997). ] (Heap, 2010).…”

“…The pollinator parents are "R" lines, as they restore fertility in a CMS derived hybrid, yet the R is rarely included in the nomenclature. R91 is the fi rst ACCase herbicide-resistant S. halepense biotype identifi ed in the literature and was included in this study as a reference point to compare mutations in DNA sequencing experiments (Smeda et al, 1997 . Herbicide selection was conducted on seedlings 7 to 14 cm tall using a bench top sprayer, which delivered 187 L ha -1 at 138 kPa using a single TEEJET 80015 LP nozzle (TeeJet, Dillsburg, PA).…”